Such a drilling tool is disclosed in the GB 2 132 667 A1 document. This drilling tool has a displacing head formed with smooth exactlie frustoconical lower and upper portions. Due to the large surface contact between the displacing head and the soil large forces are required to rotate and advance the drilling tool.
The object of the present invention is to improve a drilling tool of the displacement type so such that the drive unit acting on the drilling tool needs to provide smaller forces in at least one of the two feed directions (circumferential direction, axial direction).